Reverse total hip replacement

ABSTRACT

A reverse total hip prosthesis is characterized by a femoral cup component and an acetabular ball component and is used for reconstruction of a hip joint. The prosthesis reverses the mechanics across the joint medializing the center of rotation, preventing dislocation in a posterior direction. Both ball and socket portions of the components lie outside of bone enabling larger sizing of the femoral and acetabular components improving stability, regardless of the size of the patient&#39;s anatomy. A method for reverse hip prosthesis implantation eliminates reaming through the base of the acetabulum preserving acetabular bone stock.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a Divisional of an earlier-filed application,U.S. Ser. No. 15/225,873 entitled “Reverse Total Hip Replacement” in thename of Nicholas John Loffredo and filed Aug. 2, 2016, which claimspriority to U.S. Provisional Application No. 62/282,472 filed Aug. 3,2015, also in the name of Nicholas J. Loffredo.

FIELD OF THE INVENTION

The invention relates generally to a hip replacement arthroplasty withthe reversal of the traditional components. More specifically, theinvention relates to a reverse total hip replacement with a femoralcomponent that has a cup shaped articulating surface and an acetabularcomponent that is characterized as a spherical segment having aspherical articulating surface portion.

BACKGROUND OF THE INVENTION

In regards to total hip arthroplasties Themistocles Gluck attempted thefirst hip femoral head arthroplasty with ivory implants in 1891 (Brand,Mont, & Manring, 2011). Since that time the total hip replacement hasundergone a continually evolving spectrum of advancements in medicalscience. The evolution of the total hip replacement has led componentsto become stronger, more versatile, and wear resistant. Today's totalhip replacements are said to potentially last indefinitely by theirmanufacturers. The total hip replacement has been at the center ofmedical technical advancements from perfecting the technique of hipsurgical approaches to recent innovations in medications that reduceoperative blood loss.

In 2006 the FDA approved the Birmingham Hip Resurfacing system (Canale,2008). This new prosthesis allowed for a hip replacement withoutresection of the femoral neck. The femoral component allows for lessbone resection than a total hip replacement. Many orthopedic surgeonsbegan using this new innovative prosthesis until clinical studies showedan increase risk of femoral neck fracture in women (Powell, Belzile,Antoniou, et al., 2014). This is an important lesson that not allmedical advancements are truly the next gold standard but each canprovide an important step forward nonetheless, even if by trial anderror.

The current standard total hip replacement is made from achromium-cobalt alloy with two main components. The femoral componentconsists of a femoral intramedullary stem and neck with interchange headattachments. The femoral component has a spherical articulating head.The acetabular component is typically a metal alloy cup with a plasticpolymer inner cup insert. The femoral component recreates the ball ofthe joint while the acetabular component recreates the cup.

The surgical procedure involved to insert the total hip replacementinvolves creating an osteotomy at the base of the femoral neck andreaming the intramedullary canal to implant the femoral component. Theacetabular component is prepared by using sequential hemi-sphericalreamers to prepare an acetabular bed that mimics the dimensions of theacetabular component.

A major source of focus of design modifications with the current totalhip replacement is to minimize the rate of dislocation. Currently thedislocation rate in the US in regards to total hip replacements is 1-2%(Brown & Neumann, 2004). This is not a large number but for thosepatients unfortunate enough to experience a dislocation therepercussions can be devastating. Currently modifications to the totalhip replacements include the use of large femoral heads, proper cupalignment, and thinner cup liner to accommodate the larger femoralheads. A potential solution for solving the problem of total hipprosthesis dislocation is to reverse the design of the components.

The concept of a reverse joint prosthesis has been previously describedin patent US20070173945 by applicant Zimmer Technology, Inc. This designutilizes a reverse joint prosthesis of the shoulder. The shoulder jointprosthetic system shows a glenosphere component implanted into thehumerus. This component then articulates with a humeral cup componentwhich is implanted into the glenoid. This design is referred tocurrently as a reverse total shoulder prosthesis. The reverse totalshoulder prosthesis is currently indicated for use to restore shouldermotion in patients with advanced rotation cuff disease (Drake, G.,O'Connor, D., Edwards, T. (2010). Indications for Reverse Total ShoulderArthroplasty in Rotator Cuff Disease. Journal of Clinical Orthopedics,468(6).). This teaching of the shoulder joint prosthetic system makes nomention of the use of this prosthesis in the hip joint.

Implanting this device into the hip joint would most certainly fail fora multitude of reasons. The glenoid component is a stemmed componentthat utilizes a press-fit technique to gain bony purchase. This glenoidcomponent could not be implanted into the acetabulum because of thelimited bone stock in the medial wall of the acetabulum. The proximalhumerus does not have a narrowing or neck below the articular surface.Therefore, this design would not be suitable for the hip because thefemoral head has an anatomic neck which aligns the articular surface at125 degrees from the shaft. This allows for stability through the jointwith weight bearing.

The concept of a reverse total hip prosthesis has been described inpublication US20110218637 by applicant Zafer Termanini in 2010. Thepatent design utilized an interlocking reverse hip prosthesis. A similarinterlocking reverse total hip prosthesis was described in US20140025178by applicant Hip Innovation Technology Llc in 2013. The interlockingdesign means that the acetabular and femoral components are joinedtogether. The concept is beneficial because in theory this wouldeliminate the chance of dislocation. In reality the use of interlockingor constrained total hip prosthesis has widely fallen out of favor. Thefailure rate in long term follow up associated with constrained totalhip prosthesis has been shown to be as high as 42 percent (Yang,Goodman, 2009). This failure is a result of loosening of the acetabularcomponent which is ultimately pulled away from the pelvis secondary tothe interlocking design (Yang, C., Goodman, S B. (2009). Outcome andComplications of Constrained Acetabular Components. Journal ofOrthopedics, 32(2).).

A reverse total hip prosthesis was also described in U.S. Pat. No.8,747,481 by applicant Brian Ted Maurer in 2012. This design did notinclude an interlocking system, though, this design has many practicallimitations for clinical use. In the patent drawings, FIG. 12, elements120 and 102 articulate with each other. In reality the design of theinteraction between these two surfaces will entrap soft tissue and scarformation. Furthermore, this design is especially prone to acetabularloosening because element 118 of the FIG. 12 creates a lever arm withweight bearing on the acetabular component base. This post will create arotational force on the acetabular base shearing it from the pelvis.

SUMMARY

The present disclosure relates to hip prostheses and methods of use forpatients with damaged hip joints that require a total hip replacement.The disclosure relates to a reverse total hip replacement and comprisesa femoral and acetabular component. This reverse prosthesis changes thefemoral component from the ball surface of the joint to the cup, and theacetabular component changes from the cup portion of the joint to theball.

This method effectively reverses the native articulating biomechanics ofthe ball and socket hip joint. The reverse total hip prosthesismedializes the center of rotation of the hip joint. Therefore, thismethod provides an advantage to the standard total hip replacementbecause the reverse prosthesis requires less force for the abductormuscles to move the joint. This can be an important advantage withrevision surgery when surrounding soft tissue is scarred or damaged fromprevious surgery or infection.

The reverse total hip replacement is advantageous because the nativedimensions of the human do not dictate the size of the femoral componentcup or acetabular ball. In the reverse total hip replacement, theseaspects of the prosthesis lie outside of the bony walls of theacetabulum, enabling the largest sized head and cup to be used in asmall individual.

The reverse total hip replacement is further advantageous in this regardbecause while the standard total hip replacement is most susceptible todislocation posterior in high flexion of the hip, the reverse total hipreplacement is not. The method of the present disclosure has the addedbenefit of effectively reversing the biomechanics of the joint.Therefore, the reverse total hip would be most susceptible to anteriordislocation which is far less common than posterior dislocation. Thehuman hip can only achieve approximately 20 degrees of extension whilethe hip flexes to over 120 degrees making posterior dislocation a morelikely culprit in standard total hip replacements.

The disclosed method also has an advantage to the standard hipreplacement because it does not require reaming of the medial wall ofthe acetabulum. This is most beneficial because this wall of theacetabulum can be thin and lead to migration of the cup into the pelvis.The medial wall of the acetabulum can be exceptionally thin ornonexistent in revision total hip replacements where previous bonereaming has already occurred. The reverse design places the ballcomponent on the acetabular side. Therefore, the acetabular reamer neednot be hemispherically shaped. The apex of the spherical portion of thereamer need not exist. Thus, the reamer can substantially take on theshape of a spherical segment, defined as a portion of a sphere that hasbeen cut by parallel planes. This enables more bone to be spared fromresection during the procedure.

The reverse total hip replacement can also enable fastener fixation ofthe acetabular component in a transverse fashion. Current practice is toplace lag screws into the cup that aim the screw trajectory into thetrue pelvis and collinear to vital organs. The reverse total hipreplacement enables screw fixation along a trajectory that traverses thecup perpendicular to the current practice path of acetabular cup screws.The inventive design does not aim fasteners directly at importantneurovascular structures and organs of the pelvis.

Thus in one aspect the disclosure relates to a reverse hip replacementprosthesis device comprising a femoral component and an acetabularcomponent for implantation into a human femur and a human acetabulumwherein the femoral component further comprises a cup portion and a stemportion for implantation to the human femur and wherein the cup portionattachably accepts a saucer-shaped spacer. The acetabular componentfurther comprises an acetabular ball which fixes to an acetabular basefor implantation into the human acetabulum, the acetabular base havingsubstantially the shape of a spherical segment at its interface with theacetabulum, thereby preserving the native thickness of the medialacetabulum. The femoral component replaces a portion of a human femurand the acetabular component replaces the acetabular human socket, andwherein the cup portion of the femoral component articulates with theacetabular ball, thereby reversing the human articulating biomechanicsof ball and socket hip joints.

In another aspect, the disclosure relates to a targeting guide foralignment of acetabular base attachment fasteners, the targeting guidecomprising an acetabular base arm for removably connection to a centralbarrel of the acetabular base. The targeting guide further comprises anattachment fastener arm for guiding the attachment fasteners into theacetabulum. The attachment fastener arm further comprises cannulatedfastener sleeves for enabling the alignment of the attachment fastenerswith respect to the orientation of the acetabular base and the desiredtrajectory of the attachment fasteners in the human acetabulum. Analternative option exists to drill the pilot holes for the screwsthrough the post guide without first placing a guide wire and subsequentdrilling with a cannulated drill. The targeting guide also comprises akeyed telescoping coupling mechanism for connecting the base arm and theattachment fastener arm, which coupling mechanism enables extension ofthe attachment fastener arm for accommodating varying amounts of softtissue, while maintaining proper alignment.

In still another aspect, the invention relates to a method for a totalreverse hip replacement comprising:

-   -   a) implanting an acetabular base having an acetabular bridge by        -   i) reaming the human acetabulum using a series of reamers of            increasing size, each having a surface comprising a partial            spherical shell and an open apex, the open apex preserving            the full thickness of the medial acetabular wall, the            reaming continuing until a bed of bleeding cancellous bone            is reached;        -   ii) orienting the acetabular base such that the acetabular            bridge is in a substantially anterior to posterior            orientation enabling optimal trajectory of acetabular            fasteners for attaching the acetabular base to the            acetabulum;        -   iii) press-fitting the acetabular base into the acetabulum;        -   iv) attaching to the acetabular base a target arm for            guiding the drilling and placement of fasteners to fasten            the acetabular component to the acetabulum, the target arm            having guide sleeves concentric and angularly aligned to            fastener tunnels within the acetabular bridge;        -   v) fastening the acetabular base to the acetabulum;    -   b) removing the target arm and fixing an acetabular ball into        the acetabular base; and    -   c) implanting a femoral component having a femoral stem portion        and a femoral cup portion into a transected femur.

These and other aspects, objects, features and advantages of the presentinvention will be more clearly understood and appreciated from a reviewof the following detailed description of the preferred embodiments andappended claims, and by reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter of the present invention, itis believed that the invention will be better understood from thefollowing description when taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a fragmentary perspective view of all of the components inarticulation with each as they are in the human body once implanted;

FIG. 2 is a simplified view showing the acetabular base component withan opening at the apex of the cup and a female assembly with keyeddepression for targeting guide attachment to central stem;

FIG. 3 shows a simplified view of the substantially hemisphericalacetabular ball component which articulates with the femoral componentcup;

FIG. 4, as in FIG. 2, shows a lateral view of the acetabular basecomponent with and without fastener holes and central stem to mate withthe FIG. 3 acetabular ball component;

FIG. 5 shows a frontal view of the femoral component with plastic insertliner;

FIG. 6 shows the plastic cup liner detached from the femoral componentbase;

FIG. 7 shows the targeting guide used for accurate placement of the 2fasteners into the acetabular component;

FIG. 8 shows the targeting guide with keyed telescoping arm with dualbarrel fastener cannulas;

FIG. 9A shows a side view an alternate version of the femoral cupcomponent with 4 locking fasteners and a central post that is housed inthe femoral neck;

FIG. 9B shows a frontal view of an alternative version of the femoralcup with the central post and 4 locking screw holes for the alternativefemoral component cup;

FIG. 10A shows a top view of the open faced acetabular reamer;

FIG. 10B shows a side view of the open faced acetabular reamer withcentral attachment;

FIG. 11 shows a side view of a proximal femur with the zone oftransverse resection of the femoral head marked with dotted lines;

FIG. 12 shows a side view of a proximal femur after the zone oftransverse resection has been completed and the reamer has been used tosaucerize the femoral head;

FIG. 13 shows a side view of the post guide used for making the posthole of the central post of the alternative femoral component; and

FIG. 14 shows a top view of the post guide with central guide thatcontains an inner and outer sleeve for application of guide wire andcannulated drill.

DETAILED DESCRIPTION

The present description is directed in particular to elements formingpart of, or cooperating more directly with, apparatus in accordance withthe invention. It is to be understood that elements not specificallyshown or described may take various forms well known to those skilled inthe art.

Referring to the Figures, wherein like numerals indicate like partsthroughout the several views, attention is first directed to FIG. 1 inwhich is shown the inventive hip replacement implants as they wouldarticulate in the human hip joint. The femoral component 16 comprises afemoral stem 18, shown in FIG. 1, which would be placed into the humanfemoral canal and the cup portion 19, shown on FIG. 1, which accepts asaucer shaped spacer 14. The femoral component 16 and spacer 14 replacesthe femoral neck and head of a human hip. FIG. 1 shows the femoralcomponent 16 with a shaft 18 to neck 9 angle of 140 degrees. Thisfemoral component shaft to neck angle may vary from 120 to 140 degrees.This range allows for the optimum weight bearing surface contact of theacetabular ball component 12. The femoral component spacer 14 attachesto the mating femoral component cup portion 19, seen in FIG. 1, througha ring 11 and groove 13 fashion. An acetabular ball 12 and a base 10replaces the articular surface of the acetabulum. The acetabular ball 12articulates with the spacer 14 of the femoral component 16.

The acetabular component base 10, femoral component stem 18, andalternative femoral component 34 are comprised of suitablebio-compatible materials. The preferred bio-compatible materials includebut are not limited to cobalt-chromium alloys, ceramic, titanium andtheir combinations. Useful ceramic materials include alumina,transformation toughened zirconia, and the like. It is important toachieve a strong bond at the prosthesis-bone interface. The surfacecharacter of the prostheses in contact with bone can be exhibit a roughtexture to encourage bony in-growth. A hydroxyapatite coating may beapplied to the rough prosthesis surfaces to further improve thebone-prosthesis bond via bony on-growth. A cement, for examplepolymethylmethacrylate (PMMA) cement, may also be employed between therough prosthesis surface and the bone surface with which it interfaces.Combinations of these approaches for improving the strength of theprosthesis bone interface may also be employed.

FIG. 2 shows the acetabular base component from top view. A centralbarrel 20 having a keyed depression 25, accepts the acetabular ball 12(not shown in FIG. 2) and an acetabular base arm 30 of targeting guide29 as shown in FIG. 7. The acetabular base 10 is substantially shaped asa spherical segment, having an opening 23, shown in FIG. 2, at its apex.An acetabular bridge 24 enables structural connection of the acetabularbase 10 to the human acetabulum. The acetabular bridge 24 has twotunnels 22 in which two acetabular fasteners 44, for example acetabularscrews as shown in FIG. 7, pass through from the targeting arm. Althoughin FIG. 7, the central barrel 20 having a keyed depression 25 as shownin FIG. 2 is shown to have a screw threading to enable targeting armattachment, it is understood that other approaches can be employed forthe purposes of the invention.

FIG. 3 is a side view of the hemisphere acetabular ball 12 whicharticulates with the femoral component 16 and spacer 14. The acetabularball 12 has a cylindrical cavity 9 that engages the central barrel 20. AMorse taper enables these two components to be hammered into placetogether forming a single engaged unit. Other means of connection of theacetabular base to the acetabular ball include a central screw or pressfit with ring and groove, and the like. The engaged component 10 and 12rest in the human acetabulum.

As shown in FIG. 4, the acetabular base shape at its portion whichinterfaces to the acetabulum 21 has substantially the shape of aspherical segment. FIG. 4 also shows the entrance points of the twotunnels 22 in which each acetabular fastener 44 (see FIG. 7) passesthrough the acetabular bridge 24, shown in FIG. 2, thereby enablingfixation of the acetabular base 10 to the human acetabulum. The centralbarrel 20 is shown as comprising a screw threading and keyed depression25 which accepts the male attachment of the acetabular base arm 30,shown in FIG. 7. Other means of fixing the acetabular base to the humanacetabulum include press fit with oversizing the acetabular base 1-2 mmin diameter when compared to the human acetabulum or screwing lag screwsdirectly into the pelvis through a hole in the spherical portion of theacetabular base.

FIG. 5 is a front view of the femoral component 16. This view shows thecup portion 19 that accepts the femoral component spacer 14. The longstem shaped portion 18, of the femoral component 16 is passed into theintramedullary canal of the proximal femur.

FIG. 6 is side view of the femoral component spacer 14, which ispreferably constructed from a biocompatible polymer material that isresistant to wear as it articulates with the acetabular ball 12 which isgenerally comprised of metal alloy. Exemplary spacer materials includepolyethylene, ultra-high molecular weight polyethylene (UHMWPE), crosslinked UHMWPE, and also ceramic, or metal alloy including but notlimited to Titanium alloy, Cobalt-Chromium alloy, Alumina-Alumina alloy,Zirconium alloy, and Oxinium alloy. Preferred acetabular ball materialsinclude metal alloy or ceramic. Useful ceramic materials includealumina, transformation toughened zirconia, zirconia toughened alumina,and silicon nitride. In the case where the femoral stem and the femoralcup are both of a metal alloy, they can be formed as a unitary integralelement. Similarly, in the case where the femoral stem and the femoralcup are both of a ceramic material they can be formed as a unitaryintegral element. Further, in the integral ceramic element, the spacer14 which articulates with the acetabular ball 12, may also be formedintegrally.

FIG. 7 shows a side view of a targeting guide 29 that enables the properalignment for the two acetabular fasteners 44, to be passed through thenear wall of the human acetabulum then through the acetabular bridgetunnels 22, and finally into the far human acetabular wall. Thiseffectively seats the acetabular base into the human acetabulum. Thetargeting guide 29 comprises acetabular base arm 30 that connects to thecentral barrel 20 of the acetabular base 10 as shown in FIG. 4. Anattachment fastener arm 35 removably connects to the acetabular base arm30 and a keyed telescoping coupling mechanism 32 accommodates thevarying amounts of soft tissue in the gluteal region while maintainingproper alignment. In a particular embodiment, the attachment fastenerarm 35 includes cannulated fastener guide sleeves 26, 27, 28. The innermost sleeve 28 accommodates a guide wire, not shown. Once guide wire isplaced sleeve 28 is removed and sleeve 27 is used to enable a drill 42for drilling a pilot hole, to pass through it in alignment with thedesired trajectory through the acetabulum and through tunnels 22 in theacetabular base shown in FIG. 2. Once the pilot hole is made, sleeve 27is removed and each of the two acetabular fasteners 44 are passedthrough the fastener guide sleeve 26 and into the acetabular base 10.The acetabular fasteners 44 gain bony purchase to the human acetabulumin the near wall 41 and the far wall 43 of the human acetabulum. Lastly,the targeting guide 29, shown in FIG. 7 is removed. In anotherembodiment, only two guide sleeves 27 and 26 are used. Sleeve 27 is usedto drill the pilot hole directly into the acetabulum without the use ofa guide wire and sleeve 26 is used to aid in alignment for the insertionof acetabular fasteners 44.

FIG. 8 is a front view of the targeting arm with a keyed telescopingcoupling mechanism 32 that enables extension of the attachment fastenerarm. The targeting arm attaches to the acetabular base and the fastenerarm 35 holds the sleeves 26, 27, 28. The outer most sleeve, fastenerguide 26 is not removable and is adjoined to the attachment fastener arm35.

FIG. 9A is an alternative femoral component 34 that replaces the humanfemoral head. This femoral component 34 has an advantage in that lessbony resection is necessary for its implementation. The alternativefemoral component 34 requires a cut through the base of the femoralhead, instead of a cut at the base of the femoral neck.

Therefore, the alternative femoral component 34 allows for more bonestock preservation. The alternative femoral component stem 36 may have avariable angle of projection in a 20 degree arc to enable optimum weightbearing contact with the acetabular component 12. The femoral componentspacer 14 can be of identical or similar design for the alternativefemoral component 34. The alternative femoral component 34 has throughholes 40, seen in FIG. 9B, near the apex of the cup to enable fasteners31, to be placed into the femoral neck thereby gaining bony purchase.The fasteners 31 may be screws, for example locking screws, orcompression screws or other suitable fasteners. A preferred number offasteners 31 and matching holes 40 is 3-4. Preferably, a combination oftwo locking and two compression screws is used. A femoral neck stem 36can be press fit into the center of the human femoral neck. The femoralneck stem can be in the range of 0.3-3 cm in diameter and 3-10 cm long.The neck stem 36 is implanted into the femoral neck, and the jointgeometry dictates that axis of the neck stem is at an angle with respectto the axis of symmetry of the alternative femoral component 34. Therange of useful angles is from about 120 to about 140 degrees. A neckreamer corresponding to the size of the femoral neck stem 36 is used toprepare the human femoral neck to accept neck stem 36.

FIG. 9B is a top view of the alternative femoral component which acceptsa femoral component spacer 14 and enables the fasteners 31 shown in FIG.9A to be placed through the cup. Four through holes 40 for fasteners 31are shown in the embodiment depicted in FIG. 9B. The femoral componentspacer 14 attaches to the mating femoral component cup portion 19 (seeFIG. 1) through a snap ring 11 and groove 13 fashion. The femoralcomponent spacer 14 attaches to the mating alternative femoral component34 through a snap ring 11 and groove 55 fashion. The alternative femoralcomponent 34 is preferably made of a metal alloy.

FIG. 10A is a top view of the open faced acetabular reamer used to placethe acetabular base 10. The reamer having the shape of a sphericalsegment has an open face 62 at the apex. The surface of the reamer 45,seen on FIG. 10B, has semicircular cutting protrusions 50 that reams thebone of the acetabulum away. In a preferred embodiment, there are 4radial supports 48 that adjoin to the cylindrical attachment site 46.The attachment site 46 attaches to a stem extension that attaches to apower drill.

FIG. 10B is a side view of the open faced acetabular reamer toillustrate the semicircular cutting protrusions 50 of the reamer.

A particular method of placing the alternative femoral component beginsby making a transverse cut across the approximately central to theapproximately proximal third of the femoral head, as shown in FIG. 11.This cut may be made with an oscillating saw. Next the remainingproximal third of the femoral head is saucerized as shown in FIG. 12,using a hemi-spherical reamer that attaches to a stem and power drill.The beginning reamer size matches the smallest component sized diameter.Each reamer is used sequentially in increased diameter until a match isachieved with the desired variably sized component. Next, the post guide59, shown in FIG. 13, is placed into the saucerized femoral head and aguide wire (not shown) is placed through central guide 63, shown in FIG.13. Once the guide wire is placed, central sleeve 65, shown in FIG. 14is removed and a cannulated drill is used whereby drilling is guided bythe guide wire and the central guide 63. An alternative method exists todrill through the post guide 59 without previous placement of a guidewire. Next, post guide 59 is removed. Then the alternative femoralcomponent 34 shown in FIG. 9A is hammered into place forming a press fitusing an impactor and mallet. Once the alternative femoral component 34is seated a drill is used to make pilot holes (not shown) in the femoralbone for the four fasteners 31, as shown in FIG. 9B. A cannulated drillguide sleeve similar to that discussed above can be used inthrough-holes 40 to facilitate the accurate drilling of the pilot holes.Once the fasteners 31 are tightened into place the femoral componentspacer 14 is snapped into place using a snap ring and groove design, asshown in FIG. 9A. Similarly, a ceramic spacer would be inserted througha snap ring and groove design.

The method of placement for the acetabular base component begins byusing the open faced acetabular reamer 52, shown in FIG. 10B. Startingwith the smallest size and sequentially reaming with increasing sizeddiameter reamers, proceed until a bed of bleeding cancellous bone isreached. The bleeding bed of cancellous is optimal to facilitate bonyingrowth into the porous coated acetabular base component surface thatcontacts the human acetabular wall. The inventive acetabular reamer 52,having a surface generally comprising a partial spherical shell and anopen face 62 as shown in FIG. 10A. Thus reamer 52 does not ream away thethin medial wall of the acetabulum. Once a proper size is reachedthrough reaming, the acetabular base component 10, as shown in FIG. 4,is press fit into position using an impactor that connects to thecentral barrel 20 and mallet. The acetabular bridge 24 should beoriented in an anterior to posterior or near transverse orientation whenimpacted, as shown in FIG. 2. This enables proper trajectory of theacetabular fasteners 44. Once the acetabular base component 10 iswell-seated, an option exists for extra fixation with fastener/s placedthrough the acetabular bridge tunnels 22, as shown in FIG. 2.

Once the acetabular base component 10 is well-seated, the targeting armcan be attached to the central barrel 20, as shown in FIG. 7. Once thetargeting arm is fastened into place using targeting arm screw 8,attention is taken to the cannulated screw guide sleeves 26, 27, 28,shown in FIG. 7. Optionally, placement of a guide wire, not shown,through the inner most sleeve 28, can be used in the case thatacetabular fasteners 44 comprise cannulated screws, not shown, as isknown in the art. A retractor is placed posteriorly to protect thesciatic nerve. Once the guide wire is placed through the posterior 41and anterior 43 walls of the human acetabulum, a pilot hole is drilled,as shown in FIG. 7. The inner most sleeve 28 is removed and a cannulateddrill 42 is used to drill the pilot hole along the path of the guidewire. The guide wire passes through the lumen of the cannulated drilland drilling stops once the anterior acetabular wall is breeched. Thedrill hole is slightly smaller than the diameter of the screw. Next thedrill cannula sleeve 27 is removed leaving only the outer screw guidesleeve 26, as shown in FIG. 7. The cannulated acetabular screw 44 passesover the guide wire until the distal tip as shown in FIG. 7 has gainedbony purchase in the anterior cortical bone 43 of the human acetabulum.Once the screw/s 44 are placed the targeting arm is removed and theacetabular ball 12 is press fit along the Morris taper of the centralbarrel 20 with impactor and mallet, as shown in FIG. 1.

The invention has been described in detail, with particular reference tocertain embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described above.

What is claimed is:
 1. A method for a total reverse hip replacementcomprising: a) implanting an acetabular base that is formed as aspherical segment having a spherical interface surface that extendsbetween a first flat surface and a second flat surface parallel to thefirst flat surface and having fastener tunnels that extend in parallelto the first and second flat surfaces and through a bridge portion ofthe acetabular base, by: i) reaming a human acetabulum to reachcancellous bone using a series of reamers of increasing diameter, eachreamer having a surface comprising a partial spherical shell and an openapex formed to preserve thickness of a medial acetabular wall; ii)orienting the fastener tunnels of the acetabular base to define ananterior-to-posterior fastener trajectory within the acetabulum; iii)press-fitting the acetabular base into the acetabulum, according to thedefined anterior-to-posterior fastener trajectory; iv) fastening theacetabular base to the acetabulum; b) fixing a substantially hemisphericacetabular ball into the acetabular base; c) implanting, into atransected femur, a femoral stem portion of a femoral component, whereinthe femoral component further comprises a cup-shaped portion; and d)fitting the cup-shaped portion of the femoral component against thesurface of the acetabular ball.
 2. The method of claim 1 wherein fixingthe acetabular ball into the acetabular base comprises using a taperedfitting.
 3. The method of claim 1 wherein fixing the acetabular ballinto the acetabular base comprises using a keyed fitting.
 4. The methodof claim 1 wherein fixing the acetabular ball into the acetabular basecomprises using a fastener.
 5. The method of claim 1 further comprisingattaching a saucer-shaped spacer to the cup-shaped portion of thefemoral component.
 6. The method of claim 5 wherein attaching the spacercomprises using a snap ring and groove fastening.
 7. The method of claim1 wherein fastening the acetabular base to the acetabulum furthercomprises: attaching a targeting guide to the acetabular base, whereinthe targeting guide aligns one or more cannulated guide sleeves to thefastener tunnels of the acetabular base according to the definedfastener trajectory; drilling a hole into the acetabulum for each of oneor more fasteners, guided by the one or more guide sleeves of thetargeting guide, and removing one or more of the guide sleeves;attaching a fastener through the drilled hole, guided by one or moreremaining guide sleeves.
 8. The method of claim 7 wherein attaching thetargeting guide comprises using a threaded fitting.
 9. The method ofclaim 7 wherein attaching the targeting guide comprises connecting anarm of the targeting guide to a central barrel that extends outward fromthe acetabular base.
 10. A method for a total reverse hip replacementcomprising: a) implanting an acetabular base that is formed as aspherical segment having a spherical interface surface that extendsbetween a first flat surface and a second flat surface parallel to thefirst flat surface and having fastener tunnels through a bridge portion,the tunnels extending in parallel to the first and second flat surfacesby: i) reaming a human acetabulum to reach cancellous bone using aseries of reamers of increasing diameter, each reamer having a surfacecomprising a partial spherical shell and an open apex formed to preservethickness of a medial acetabular wall; ii) orienting the tunnels of theacetabular base to define an anterior-to-posterior fastener trajectorywithin the acetabulum; iii) press-fitting the acetabular base into theacetabulum, according to the defined fastener trajectory; iv) attachinga targeting guide to the acetabular base, wherein the targeting guidealigns one or more cannulated guide sleeves to the fastener tunnels ofthe acetabular base according to the defined fastener trajectory; v)drilling into the acetabulum for each of one or more fasteners, guidedby the one or more guide sleeves of the targeting guide; vi) removingone or more of the guide sleeves; vii) attaching the one or morefasteners, guided by one or more remaining guide sleeves, to fasten theacetabular base to the acetabulum; viii) removing the targeting guidefrom the acetabular base; b) fixing a substantially hemisphericacetabular ball into the acetabular base; c) implanting, into atransected femur, a femoral stem portion of a femoral component, whereinthe femoral component further comprises a cup-shaped portion; and d)fitting the cup-shaped portion of the femoral component against thesurface of the acetabular ball.